Fig. 7. Downregulation of SoxB1 mRNA in vegetal blastomeres requires ß-catenin, but not Krl. Zygotes were injected with glycerol (control), with mRNA encoding the indicated mRNAs, or with Krl-MO, allowed to develop to the hatched blastula stage, and then assayed by whole-mount in situ hybridization with a SoxB1 probe. (A) Blocking nuclearization of ß-catenin by injection of C-cadherin mRNA blocks downregulation of SoxB1 mRNA in vegetal blastomeres. (B) Neither knockdown of Krl translation with a KrlMO nor its mis/overexpression by mRNA injection (Krl MOE) detectably affects downregulation of SoxB1 message in vegetal blastomeres. However, in the animal hemisphere, loss of Krl function leads to a decrease in SoxB1 mRNA, whereas MOE up regulates it. This effect is likely to reflect the operation of the SoxB1 negative-autoregulatory loop, as discussed in the text and illustrated in Fig. 5. Scale bar: 20 µm.